The present embodiments relate to electronic signal processing circuits and are more particularly directed to a circuit for generating a noise signal having a Guassian probability distribution function (“PDF”), for use in implementations where such a noise signal is desired or useful, such as in circuit testing applications.
Electronic circuits have become prevalent in numerous applications, including uses for devices in personal, business, and other environments. Demands of the marketplace affect many aspects of circuit design, including factors such as device complexity and cost. Various electronic circuits are directed to signal processing and, quite often, these circuits also are subject to these design factors. Often in testing components such as audio components, whether in design testing or through auto-testing, one or more source signals are generated with known characteristics, where one of these signals is then applied to a device so that the response to the signal may be evaluated, thereby providing data to characterize the device. In audio processing, one type of favorable source signal is a white noise signal having a Gaussian PDF. Such signals are often preferred for various reasons. For example, such a signal has a relatively flat signal spectrum density. As another example, such a signal has a very low autocorrelation at non-zero lag. As still another example, a linear operation applied to such an input signal produces an output signal that also has a Gaussian PDF. Each of these attributes often simplifies or renders more usable the testability of a device subject to a signal with these attributes.
The prior art has described circuits for providing a signal, such as to be used for a test signal, and having a Gaussian PDF. For example, one such circuit implements a random number generator, where the initially generated output alone may provide a relatively flat PDF. However, the initially generated output is then sampled by an algorithm that provides a modified output, where the modified output includes some values that are the same as sampled from the initially generated output, while other values in the modified output are substituted in place of corresponding samples in the initially generated output. More specifically, the algorithm samples the initially generated output and in some instances passes the sample out as part of the ultimate output where, in other instances and provided the sample is within a certain range, the algorithm substitutes a differing value in place of the sample and outputs this differing value. Accordingly, the series of ultimate outputs signals comprise both passed input samples as well as some substituted values, thereby forming a collection of samples having a Gaussian PDF.
While the above-described algorithm for producing a signal with a Gaussian PDF has proven workable in various implementations, the present inventor has determined that in certain situations an alternative may be favorable. For example, in some audio processing contexts, an audio processing circuit may include various circuitry that exists for certain signal processing purposes; such circuitry may include signal sources, such as for use in audio dithering, and also signal filters. The present inventor has further recognized that these devices may be further configured and programmed in order to provide a resulting output white noise signal having a Gaussian PDF without the need for circuitry, software, and/or firmware to implement the above-described algorithm. Thus, device complexity and cost may be reduced as compared to a design requiring additional architecture to implement the prior art approach. In addition, one skilled in the art will appreciate other instances in which the preferred embodiments may more favorably provide an output white noise signal having a Gaussian PDF over those used in the prior art.